Rock blasting is one of the initial steps of the production process in the mining industry. The main objective of a rock blasting operation is to maximize the extraction of raw material while minimizing the costs and the environmental impact of the operation. In general, the operation of rock blasting is performed by the detonation of chemical explosives placed on or in tubular holes on a rock mass.
The rock blasting operation is performed according to a “blast plan” prepared under the supervision of engineers with experience in mine planning. The blast plan defines a set of controllable parameters, such as: diameter, spacing and depth of the explosive holes, load mass of the explosives, spatial distribution of the explosives and chronological sequencing of the explosions.
To optimize the rock blasting operation, the technique of sequential detonation is frequently used. This technique makes use of delay in the blasting activities, controlling the time lag between the firing of explosive charges. The nature of the shock waves resulting from the explosion, in association with the time interval between detonations, leads to interference patterns among the shock waves. These interferences can be used to benefit the mining process, providing higher quality to the rock blasting operation.
The appropriate chronological sequencing of the explosions minimizes unwanted vibrations, facilitates the fragmentation of the rocks, and is of great importance in underground mining operations.
Besides the chronological sequencing detonations, other controllable variables in the blast plan include: the diameter, spatial distribution, spacing and depth of the holes and the load mass of the explosives.
On the other hand, examples of uncontrollable variables of the blast plan are: the weather conditions and the ground geology.
It is known that the propagation of mechanical waves depends strongly on the geology of the land. Hence, a good blast plan has to consider the structure of the rock mass and its properties and also has to take into account its mechanical reaction to the blasts and other external conditions.
A blast plan that does not consider such uncontrollable variables can lead to poor fragmentation, may damage the adjacent walls of the quarry and may increase environmental impacts and operational costs.
Nevertheless, the exact determination of the geological conditions of a specific terrain is very difficult and expensive to ascertain and sometimes may even be unpractical, e.g. outer space mining. The samples of materials tested in a laboratory before the development of the blast plan exclude discontinuities and unforeseen lithological changes in the rock mass from which they came.
The prior art also includes several tools and techniques designed to improve the blast plan. These techniques (usually of empirical nature) include several formulas involving geometric patterns and may make use of old-fashioned tools such as abacus and slide rules. Anyhow, these methods often ignore a large number of variables that influence the quality of the rock blasting.
Another drawback of the blast plan of the prior art is that, once triggered, it cannot be corrected during the process of detonation. In case of unsatisfactory results, the development of a new blast plan is required. FIG. 1 illustrates a prior art operational process 100 of rock blasting.
In the prior art, the activation of the explosive charge is performed by means of an initiation system. The initiation system (also known as a “trigger”) can be any of the following devices: a non-electrical trigger, an electrical trigger, an electronic trigger or a wireless trigger.
Among these four devices, the most popular in the mining industry are the electrical and electronic triggers. Both allow the timing control of the explosion, especially the electronic triggers, which have very precise timers and control means.
As for the non-electrical trigger and the wireless trigger, the former one has become obsolete and the latter one, until recently, was almost exclusive to military operations. Nowadays, the explosives industry is starting to take advantage of the ever decreasing sizes and costs of the wireless electronic devices available on the market. The wireless components available these days are so small and inexpensive that they might be considered expendable. The main benefits of the wireless sensor is the higher distance provided from the controllers to the explosives (which implies higher safety standards) and the possibility of abortion of the rock blasting operation at any given time. The prior art wireless sensors usually employ conventional bidirectional radio systems (VHF or UHF).
The prior art document WO/2001/059401 reveals a wireless detonation system that employs radio transmitters to activate a wide range of detonators placed near to explosive loads disposed inside of a rock mass. The technology of WO/2001/059401 comprises a main controller (a computer disposed near a blast operator employee) and a radio frequency base transmitter (disposed nearby the rock mass). The main controller coordinates the timing of explosions and delivers electronic signals to the RF Base Transmitter, which, in turn, sends radio commands to the detonators of the explosive loads spread across the rock mass.
One of the shortcomings of the technology disclosed in WO/2001/059401 is that the detonation system does not account for the discontinuities and unforeseen lithological changes in the rock mass that may lead to an inefficient blasting operation. Furthermore, conventional charges do not have embedded intelligence, communication and sensing capabilities.